Method and apparatus for reference time acquisition for positioning reference signals in a wireless communication network

ABSTRACT

The present invention provides a muting configuration for reference signal (RS) transmission as a pattern defined by at least the combination of a muting sequence and a reference point. Muting occasions for a given wireless communication network cell thus are differentiated from another cell by use of a different muting sequence, a different reference point, or both. Moreover, in one or more embodiments, the present invention provides for the use of a common muting sequence or reference point across cells, with muting occasions being differentiated between cells through use of different reference points (in the case of a common muting sequence), or through use of different muting sequences (in the case of a common reference point), or different sequences and different reference points. Such arrangements simplify the signaling needed to control or indicate the muting configuration in use in the cells of interest, provide an advantageous basis for propagating muting configurations among cells, eliminate the need for predefined muting configurations, and the need for blind detection of muting by wireless communication apparatuses, such as UEs.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/936,931, filed Nov. 10, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/643,348, filed Oct. 25, 2012, now U.S. Pat. No.9,213,080, which is a National Stage Entry of PCT/SE2010/051349, filedDec. 7, 2010, which claims the benefit of U.S. Provisional PatentApplication No. 61/328,752, filed Apr. 28, 2010, the disclosures ofwhich are fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to interference management inwireless communications networks and in particular to signaling supportassociated with the muting of reference signals for interferencereduction in wireless communication networks that transmit referencesignals, e.g., for positioning measurement.

BACKGROUND

The possibility of identifying user geographical location in the networkhas enabled a large variety of commercial and non-commercial services,e.g., navigation assistance, social networking, location-awareadvertising, emergency calls, etc. Different services may have differentpositioning accuracy requirements imposed by the application. Inaddition, some regulatory requirements on the positioning accuracy forbasic emergency services exist in some countries. Emergency 911 servicesin the U.S. (FCC E911) stands as one example of regulation-drivenrequirements.

In many environments, the position can be accurately estimated by usingpositioning methods based on GPS (Global Positioning System). Nowadaysnetworks also often have a possibility to assist items of user equipment(UEs), to improve their receiver sensitivity and GPS startup performance(referred to as Assisted-GPS positioning, or A-GPS). GPS or A-GPSreceivers, however, may not necessarily be available in all wirelessterminals. Furthermore, GPS is known to often fail in indoorenvironments and urban canyons. A complementary terrestrial positioningmethod, called Observed Time Difference of Arrival (OTDOA), hastherefore been standardized by 3GPP.

With OTDOA, a terminal measures the timing differences for downlinkreference signals received from multiple distinct locations. As anexample, a particular UE receives downlink reference signals from asupporting or reference cell, and from a number of neighboring cells.For each (measured) neighbor cell, the UE measures a Reference SignalTime Difference (RSTD) which is the relative timing difference between aneighbor cell and the reference cell. The UE position estimate is thenfound as the intersection of hyperbolas corresponding to the measuredRSTDs. At least three measurements from geographically dispersed basestations with a good geometry are needed to solve for two coordinates ofthe terminal and the receiver clock bias of the terminal. Positioningcalculations can be conducted, for example, by a positioning server(E-SMLC or SLP in LTE) or UE. The former approach corresponds to theUE-assisted positioning mode, whilst the latter corresponds to theUE-based positioning mode.

To enable positioning in LTE and facilitate positioning measurements ofa proper quality and for a sufficient number of distinct locations, newphysical signals dedicated for positioning (positioning referencesignals, or PRS) have been introduced and low-interference positioningsubframes have been specified in 3GPP. See 3GPP TS 36.211, EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation, for more detailed information on PRSs.

Broadly, PRSs are transmitted according to a predefined pattern andfollowing one of the predefined PRS configurations, each defined by: aPRS transmission bandwidth, the number of consecutive positioningsubframes (N_(PRS)) defined as a PRS positioning occasion, and a PRSoccasion periodicity of T_(PRS), measured in subframes, i.e., the timeinterval between two positioning occasions. FIG. 1 depicts thisdefinitional arrangement for subframe allocation in a given networkcell. (Note that a “cell” refers to a defined coverage area, e.g., underthe control of a given base station. Each base station within the radioaccess portion of the network may control one cell, or more than onecell, but reference signals generally are transmitted for each suchdistinct cell.) The values currently allowed by the standard of T_(PRS)are 160, 320, 640, and 1280 subframes, and the number N_(PRS) ofconsecutive subframes are 1, 2, 4, and 6 (again, see 3GPP TS 36.211).

Because OTDOA positioning requires measuring PRS signals from multipledistinct locations, the UE receiver must be able to handle the casewhere some of the PRSs are received at much weaker signal levels. Forexample, the PRS from a given neighboring cell may be much weaker at theUE than those from the serving cell. As a further complication, a UEwithout approximate knowledge of when the PRSs are expected to arriveand according to what pattern is obligated to perform signal searchingwithin a large window. Such processing affects the time and accuracy ofthe measurements, and undesirably increases UE complexity.

Therefore, to facilitate PRS measurements by UEs, the network transmits“assistance data.” Among other things, the assistance data includesreference cell information, neighbor cell lists containing PC's(Physical Cell IDs) of neighbor cells, the number of consecutivedownlink subframes occupied by PRSs, PRS transmission bandwidth,frequency, etc.

However, as another complication related to PRS measurement, the PRStransmitted by any given cell can be transmitted with zero or very lowpower, both of which may be referred to as muting. Muting applies to allPRS resource elements within a certain time period (e.g., one subframeor one PRS positioning occasion) over the entire PRS transmissionbandwidth. PRS muting provides a mechanism to reduce interference in PRSmeasurements, e.g., muting PRS transmission in one cell allows UEs tomake better measurements on the PRS transmitted in another cell. Whilestandardized approaches to PRS signaling may exist, no suchstandardization exists with regard to particular muting patterns used.

Certain approaches to muting have been discussed in the context of 3GPP.One approach relies on random muting by cells, where each base station(eNodeB in LTE) decides whether its PRS transmissions are muted or notfor a given positioning occasion according to some probability. In asimple or random implementation, there is no coordination among eNodeBsand the probability is statically configured per eNodeB or per cell.Random muting offers the advantage that no signaling is needed, as eacheNodeB makes muting decisions autonomously, according to the configuredprobability. However, the approach has disadvantages.

For example, real-world networks are not homogeneous. They havedifferent cell coverage areas and user densities, and possibly differenttypes of base stations. These variations imply that setting optimalmuting probabilities is a tedious task. Further, random muting does notprovide UEs with information on whether a cell is or is not muted for agiven positioning occasion, which complicates RSTD measurements andincreases the UE complexity. Still further, the optimal configuration ofthe muting probabilities may also vary, for example, over the day andover the week and on the cell basis, which makes static configurationsnot the best option from a practical point of view.

Another approach provides a limited set of muting patterns and mapsthose patterns to PCTs. See, for example, the proposals provided asR1-093793, Muting for LTE Rel-9 OTDOA Positioning, 3GPP TSG-RAN WG1meeting #58bis, October 2009, and as R1-092628, On serving cell mutingfor OTDOA measurements, 3GPP TSG-RAN WG1 meeting #57, June 2009.

One advantage of the above mapping-based approach is that given a tableof muting patterns and PC's received in the assistance information, anygiven UE can determine when the PRSs are muted in a given cell ofinterest without the muting information being explicitly signaled to theUE. However, as a disadvantage, the muting patterns need to be eitherhard coded in UEs (which implies the solution is not suitable for allUEs) or received from the network for which new signaling would berequired.

As a further complication, mapping muting patterns to PC's will mostlikely not result in an optimal muting configuration in non-uniform realnetworks that may also have a multi-layer structure. In other words,such a mapping-based muting configuration would be fixed and thusimpossible to re-optimize unless PCI planning is redesigned for theentire network specifically for positioning, which is most likely to bethe least desired activity from the network operator's point of view.

Other proposals involve the transmission of muting indicators to UEs,indicating whether or not autonomous muting for a given cell isactivated. See, e.g., 3GPP RP-100190, Autonomous muting in DL OTDOA,Motorola, March 2010, and see CR to 3GPP TS 36.355, Autonomous mutingindication in OTDOA assistance information, Motorola, March 2010.According to such approaches, a Boolean indicator is transmitted for thereference cell and also all neighbor cells, as a part of the assistancedata whenever PRSs are transmitted. When the indicator is FALSE, UEs canavoid blind detection of PRS muting, optimize detection thresholds andthus improve the positioning performance. With the indicator set toTRUE, the UE still does not receive the information on when and in whichresource blocks (RBs) muting occurs, which means that the UE still needsto blindly detect when PRS muting is used in each cell, i.e. theproposal does not solve the problems associated with blind detection.

As an alternative that simplifies UE requirements, it has been proposedto remove autonomous muting functionality from the LTE Rel. 9specification. However, such a proposal leaves unaddressed thosescenarios which have been shown to require muting.

SUMMARY

In one or more embodiments, the present invention defines the mutingconfiguration for reference signal (RS) transmission as the combinationof a muting sequence and a reference point. Muting times—also referredto as muting occasions—for a given cell thus can be differentiated fromanother cell by use of a different muting sequence, a differentreference point, or both. Moreover, in one or more embodiments, thepresent invention provides for the use of a common muting sequence orreference point across cells, with muting occasions being differentiatedbetween cells through use of different reference points (in the case ofa common muting sequence), or through use of different muting sequences(in the case of a common reference point). Such arrangements simplifythe signaling needed to control or indicate the muting configuration inuse in the cells of interest, provide an advantageous basis forpropagating muting configurations among cells, eliminate the need forpredefined muting configurations, and the need for blind detection ofmuting by UEs or other receivers.

Further, one or more embodiments of the present invention provide a setof alternative solutions for defining reference points, and provide amethod for transforming between different muting configurations, e.g.,by shifting a base muting sequence differently in each of a number ofcells, such that each cell uses a differently-shifted version of thebase sequence. Still further, one or more embodiments of the presentinvention provide for signaling login between different types of networknodes, to enable the exchange and optimization of muting configurations.

Accordingly, in one or more embodiments, the present invention providesa method in a wireless communication apparatus of determining times whenperiodically-transmitted reference signals are muted in a cell of awireless communication network. The method includes determining aperiodic muting sequence indicating a muting pattern used for muting thereference signals in the cell, and determining a reference pointrelating the periodic muting pattern to a certain reference time. Themethod further includes determining when the reference signals are mutedin the cell according to the periodic muting sequence and the referencepoint.

Correspondingly, a wireless communication apparatus comprises a receiverconfigured to receive signals from the wireless communication network,including reference signals periodically transmitted for a cell in thewireless communication network. The apparatus further comprises acontroller operatively associated with the receiver. The controller isconfigured to determine a periodic muting sequence indicating a mutingpattern used for muting the reference signals in the cell, and todetermine a reference point relating the periodic muting pattern to acertain reference time. The controller is further configured todetermine when the reference signals are muted in the cell according tothe periodic muting sequence and the reference point.

In another embodiment, a method is implemented in a base station that isconfigured for use in a wireless communication network. The methodincludes determining a muting configuration for a cell controlled by thebase station, where the muting configuration is defined at least in partby a muting sequence comprising a pattern for muting reference signalsperiodically transmitted for the cell. Further, the method includesmuting the reference signals for the cell according to the mutingconfiguration.

In one particular embodiment, “determining” the muting configuration atthe base station comprises the base station deciding the mutingconfiguration, and such decision making can be made singularly by thebase station, or via OAM, or cooperatively across one or moreneighboring cells (e.g., based on communicating with one or more otherbase stations controlling one or more neighboring cells). In such anembodiment, the method may further include the base station sendingsignaling to a positioning node or other node within the network,indicating the muting configuration decided on by the base station.Alternatively, “determining” the muting configuration at the basestation comprises receiving signaling indicating the mutingconfiguration decision made for the cell by another node in the network,such as a positioning or operations and maintenance node.

In correspondence with the base station method, the teachings hereinfurther disclose a base station that includes a radio communicationinterface configured to transmit signals, including reference signals(for each cell controlled by the base station). The base station furtherincludes a controller operatively associated with the radiocommunication interface. In particular, the controller is configured todetermine a muting configuration for a cell controlled by the basestation, said muting configuration defined at least in part by a mutingsequence comprising a pattern for muting reference signals periodicallytransmitted for the cell, and mute the reference signals for the cellaccording to the muting configuration. Again, the base station may“determine” the muting configuration based on receiving signaling fromanother node, indicating the decided muting configuration for the cell,or the base station may “determine” the muting configuration based on itdeciding the muting configuration (for the cell on an individual basis,or for the cell on a cooperative basis, e.g., cooperatively deciding themuting configuration for the cell as one among a set of neighboringcells).

In yet another embodiment, the teachings presented herein disclose amethod in a positioning node that is configured for operation in awireless communication network. The method includes determining a mutingconfiguration for each of one or more cells of the wirelesscommunication network, wherein the muting configurations of the one ormore cells control the times when muting is applied to reference signalsperiodically transmitted in each of the one or more cells. The methodfurther includes generating assistance data for one or more userequipments, said assistance data indicating the muting configurations ofthe one or more cells, and signaling the assistance data to the one ormore user equipments.

In one embodiment of the positioning node method, “determining” themuting configuration for each of one or more cells comprises thepositioning node deciding the muting configuration to be used for eachof the one or more cells. For example, the positioning node may decidethe muting configurations jointly, for given groups or sets ofneighboring cells, such that the muting configuration of each cellcomplements (in terms of pattern/timing) the muting configuration of aneighboring cell. In any case, in embodiments where the positioning nodeis the decision maker as regards the muting configurations, the methodfurther includes the positioning node sending control signaling to thebase station(s) associated with the one or more cells for which thepositioning node has decided the muting configurations. Such controlsignaling causes the base station(s) to adopt the muting configurations,as decided by the positioning node.

In an alternative embodiment, the base stations (or another node, suchas an operations and maintenance node) decide the muting configurationsfor the cells, and in such cases the positioning node “determines” themuting configuration of the cells based on receiving signaling thatindicates those configurations. For example, each base station signalsto the positioning node the muting configuration of each cell under thecontrol of the base station.

In an embodiment corresponding to the positioning node method, theteachings herein provide for a positioning node that is configured foroperation in a wireless communication network. The positioning nodecomprises one or more processing circuits that are configured todetermine a muting configuration for each of one or more cells of thewireless communication network. As explained earlier, the mutingconfigurations of the one or more cells control the times when muting isapplied to reference signals periodically transmitted in each of the oneor more cells, and “determining” comprises deciding on the mutingconfigurations at the positioning node, or receiving signalingindicating the muting configurations as decided on by another node ornodes in the network.

The processing circuits are further configured to generate assistancedata for one or more user equipments (UEs), the assistance dataindicating the muting configurations of the one or more cells.Correspondingly, the positioning node includes a communication interfaceoperatively associated with the one or more processing circuits, wherethe communication interface is configured to signal the assistance datato the one or more user equipments. As an example, such signalingconstitutes higher-layer positioning protocol signaling that is carried,for example, transparently through one or mode nodes, e.g. involved basestations and MME, for reception by the UEs.

Note that one or more embodiments of the positioning node method andnode hardware contemplated herein are configured to provide mutingconfiguration propagation, wherein the positioning node determines themuting sequence for one cell by cyclically shifting a given mutingsequence by a determined amount. For example, the given muting sequencemay comprise a base sequence having a reference point defined accordingto a timing in a reference cell. As an example, the timing may be aframe or sub-frame transmission timing. The positioning node“propagates” this given muting sequence (i.e., time wise shifts it intoalignment with periodic reference signal transmissions in another cell,based on the reference point and the timing of the other cell). Broadly,the positioning node is configured to work with cell-specific mutingsequences and reference points, or cell-specific reference points and acommon muting sequence, or cell-specific muting sequences and a commonreference point.

In all of the above embodiments, however, the amount of signaling neededto convey the particular muting configuration in use in a given cell issignificantly reduced. That is, the muting configuration of a given cellis defined by a muting sequence and a reference point, and a relativelysmall number of bits are needed to identify the reference point and/ormuting sequence. Indeed, in one or more embodiments, UEs may bepre-configured with a set of possible muting sequences and/or referencepoints, and signaling which muting sequence and/or reference pointapplies to a given cell can be accomplished by signaling table indexesor the like. Alternatively, rather than pre-configuring the UEs, suchtables can be signaled to each UE at call setup, or at other convenienttimes.

Of course, the present invention is not limited to the above briefsummary of features and advantages. The described embodiments, includingrearranging patterns to a common reference point performed by some nodeor propagating the muting sequence to a certain time point, may also beadopted for other purposes than positioning, e.g. when cell transmissionactivity or muting is controlled by means of transmission patterns andthe transmission activity or muting are not necessarily limited toreference signals. For example, muting may be applied to signals otherthan reference signals. Examples of other signals are signals orchannels carrying data, e.g., the Physical Downlink Shared Channel(PDSCH) in LTE.

Further, the principles and methods disclosed herein are not limited toLTE and may be well adapted in networks using one or more other radioaccess technologies.

The wireless UE described herein may be any device being positioned e.g.a wireless terminal, a laptop, a small RBS, a sensor, or a beacondevice.

Additionally, although the invention is described for radio nodesreferred to as eNodeBs, the radio nodes in the invention embodiments maybe any radio node, e.g., a macro base station, a micro base station, arelay, a beacon device, or even a wireless terminal with thecorresponding functionality in mobile-to-mobile communication networks.Positioning node described in the invention as an E-SMLC may be any nodewith positioning functionality, e.g., E-SMLC, SUPL Location Platform(SLP) in the user plane, or even a wireless terminal with thecorresponding functionality in mobile-to-mobile communication networks.

Those of ordinary skill in the art will recognize additional featuresand advantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an approach to time-wise allocation of subframesas positioning occasion subframes, for positioning reference signal(PRS) transmission in a given cell.

FIG. 2 is a block diagram of one embodiment of a wireless communicationnetwork that is configured according to the present invention.

FIG. 3 is a block diagram illustrating example embodiments of a basestation, reference signal configuration control node, and userequipment, such as would be used in the network illustrated in FIG. 2.

FIG. 4 is a logic flow diagram illustrating one embodiment of a methodimplemented in a user equipment or other wireless communicationapparatus, for determining the muting configuration used to mutereference signal transmissions in a given network cell.

FIG. 5 is a logic flow diagram illustrating one embodiment of a methodimplemented in a base station, for determining a muting configuration tobe used for muting reference signal transmissions by the base station.

FIGS. 6-8 are logic flow diagrams illustrating embodiments of methodsimplemented in a network node, such as a positioning node, fordetermining a muting configuration to be used for muting referencesignal transmissions by a given base station, or a plurality of basestations.

FIG. 9 is a diagram illustrating one embodiment of a base sequence, suchas may be used to define a muting sequence according to the presentinvention.

FIG. 10 is a diagram illustrating shifted versions of the base sequenceof FIG. 9, wherein the shifted versions operate as unique mutingsequences for defining different muting configurations in differentcells of a wireless communication network.

FIGS. 11 and 12 are example illustrations of muting sequencepropagation.

FIG. 13 is a table illustrating various combinations of unique orgeneric reference points with generic or unique muting sequences, as abasis for defining different muting configurations in different cells ofa wireless communication network.

DETAILED DESCRIPTION

FIG. 2 depicts an example wireless communication network 10, which maybe an LTE network. The example network 10 includes a Radio AccessNetwork (RAN) 12 that communicatively couples user equipment (UEs) 14 toa Core Network (CN) 16, which in turn couples the UEs 14 to each otherand/or to equipment in other external networks.

The RAN 12 includes a number of base stations 18, each of which controlsand provides radio service in one or more “cells” 20. While FIG. 2depicts a one-to-one relationship between base stations 18 and cells 20,those of ordinary skill in the art will appreciate that one base station18, e.g., an eNodeB in an LTE implementation of the network 10, may beconfigured to control more than one cell 20 in the network 10.

From FIG. 2, one also sees example entities within the CN 16. Here, theexample entities include a serving gateway (SGW) node 22, which providesrouting and other communication functions, linking the UEs 14 to otherequipment and/or networks. The CN 16 also includes a reference signalconfiguration controller (RS CFG. CONTROLLER) 24, which may be apositioning node such as an E-SMLC or SLP, or another network node, e.g.O&M or SON nodes. While referred to as a “controller,” the node 24 maynot control the muting configurations used by the base stations 18, orat least not control all elements of such configurations, but may stillact as a centralized node for receiving muting configuration informationfrom the base stations 18, and for disseminating at least a portion ofthat information to UEs 14 (and any other radio equipment receiving RSsfrom the base stations 18) via higher-layer signaling, which may bepropagated through one or more of the base stations 18.

For example, in one embodiment, the base stations 18, individually orcooperatively with each other, decide their own-cell mutingconfigurations and signal those decisions to the node 24 (which is apositioning node or operations and maintenance node, for example). Tothis end, the base stations 18 may include a type of reference signalcontroller 25, which is configured to decide the mutingconfiguration(s). In other embodiments, the node 24 is the decider ofmuting configurations for the cells 20, and it sends control signalingto the base stations 18, to indicate those muting configurationdecisions.

FIG. 3 illustrates corresponding example implementations of the UEs 14,the base stations 18, and the node 24. It will be appreciated by thoseskilled in the art that these entities may include computer-basedcircuitry, such as one or more circuits based on microprocessors,digital signal processors, ASICs, FPGAs, or other programmable orprogrammed digital processing circuitry. As such, one or more aspects ofthe operation of the illustrated entities may be implemented byconfiguring the entity via the execution of stored computer programs,held in memory or other computer-readable media in or accessible to theentity. As such, the various illustrated circuits may be implemented inhardware, software, or a combination of both.

With that in mind, a first example base station 18-1 comprises a radiocommunication interface 30 that is configured to transmit referencesignals from the base station 18-1 according to a certain referencetime, for a given cell 20 that is controlled by the base station 18-1.In this regard, it will be understood that a given type of referencesignal, e.g., a positioning reference signal, may be transmitted in agiven cell 20 on a periodic basis, and that these recurring referencesignal transmissions may be muted according to defined patterns. Theapplication of that pattern to the periodic reference signaltransmissions thus may be referenced to a certain reference time, whichprovides as a reference or logical starting point for the muting patternin relation to the reference signal periodicity. More broadly, thecommunication interface 30, e.g., a cellular communication interface,supports downlink and uplink signaling with a plurality of UEs 14.

The base station 18-1 further includes one or more processing circuits32, which at least functionally include a reference signal transmissioncontroller 34, referred to for convenience as “controller 34.” Thecontroller 34 is configured to determine muting occasions at which thebase station 18-1 is to mute its transmission of reference signals forthe given cell 20, based on being configured to: determine a mutingsequence that indicates a timing pattern relative to the referencesignal transmission periodicity, wherein said muting sequence is to beapplied by the base station 18-1, for muting its recurring transmissionof the reference signals in the given cell 20; determine a referencepoint relating the periodic muting pattern to a certain reference time;and control said radio communication interface 30, to mute thetransmission of the reference signals for the given cell 20.

Still further, the base station 18-1 includes one or more othercommunication interfaces 36 for communicating with another network nodein the network 10, e.g., with the node 24 in the CN 16. In at least onesuch embodiment, the controller 34 is configured to signal a mutingconfiguration of the base station 18-1 for the given cell 20 to anothernetwork node, wherein the muting configuration indicates at least one ofthe reference point and the muting sequence for the given cell. Forexample, the base station 18-1 may determine its muting configurationand signal that configuration to the network node 24, via thecommunication interface 36. In at least one such embodiment, thecontroller 34 is configured to determine the muting occasions to be usedby it for the cell 20 by determining the muting sequence, or thereference point, or both, in coordination with another base station(e.g., base station 18-2), based on exchanging signaling with the otherbase station. The base stations 18-1 and 18-2 each include interfacecircuitry supporting a base station interface 38, for exchanging suchsignaling—e.g., in an LTE embodiment, such information is exchangedbetween eNodeBs via the X2 interface.

In at least one embodiment where the controller 34 decides all or partof the muting configuration used by the base station 18-1, thecontroller 34 is configured to determine the muting sequence by derivinga shifted muting sequence from a base muting sequence, in accordancewith information indicating a cyclic shift to be used for deriving theshifted muting sequence. The information indicating the cyclic shift maybe received from another node in the network 10, e.g., from the node 24,or may be determined cooperatively between base stations 18 or may bepre-determined, being the same or different by cells. In any case, itshould be understood that any given base station 18 “determines” itsmuting configuration in whole or in part based on making its owndecisions about the muting sequence and reference point to use fordetermining its muting occasions (where these decisions may be madecooperatively with another base station 18), or “determines” its mutingconfiguration in whole or in part based on receiving control signalingfrom another entity (e.g., from the node 24 and/or from another basestation 18). (Note two example cases: one where the BS communicates thedecided muting configuration to the positioning node, and one where theBS communicates the decided muting configuration to the positioningtarget (e.g., a UE)).

In the case where another node in the network 10 decides all or part ofthe muting configuration to be used by any given base station 18, thatnode sends (directly or indirectly) corresponding control signaling tothe base station 18-1. For example, the reference signals transmittedfrom the base stations 18-1, 18-2, etc. comprise PRSs, to enablepositioning-related measurements to be made by wireless communicationapparatuses operating in the given cell 20, or operating in aneighboring cell 20. In at least one such embodiment, the controller 34is configured to determine the times when the reference signals aremuted (“muting occasions”) by determining the muting sequence, or thereference point, or both, based on signaling received from the node 24or from another node in the network 10.

FIG. 3 thus provides example details for the node 24. As noted, the node24 may be an E-SMLC or other positioning node configured for operationin the network 10. As illustrated, the node 24 comprises one or morecommunication interfaces 40 for communicating with at least one of abase station 18 and one or more radio receivers that receive referencesignals from said base station, e.g., one or more UEs 14. As such, thecommunication interface(s) 40 will be understood as circuitry andprotocol processors, for signaling base stations 18 and/or forgenerating higher-layer signaling that is carried through the basestations 18, but is targeted to the UEs 14 or other radio receiversrequiring muting configuration information, for measuring referencesignals from the base stations 18.

The node 24 further includes one or more processing circuits 42—e.g.,digital processing circuitry—that are configured to determine a mutingconfiguration for a base station 18. The muting configuration definesthe muting occasions at which the base station 18 is to mute itstransmission of reference signals. According to the teachings herein,the muting configuration includes information indicating at least oneof: a muting sequence that indicates a timing pattern relative to areference signal transmission periodicity, wherein the muting sequenceis to be applied by the base station 18, for muting its recurringtransmission of the reference signals; and a reference point thatindicates a logical starting period of the muting sequence, relative toa certain reference time. (It should be understood that a given basestation 18 may be in charge of several cells and may use differentmuting configurations between such cells.)

The processing circuit(s) 42 are further configured to send mutingconfiguration information to the base station 18, or to radio equipmentreceiving the reference signals from the base station 18, in accordancewith the muting configuration. That is, in “determining” the mutingconfiguration of the base station 18, the node 24 may be the entity thatdecides all or part of that muting configuration, and thus sendscorresponding control signaling to the base station 18. In suchembodiments, the node 24 also may send higher-layer signaling to the UEs14, to indicate all or part of the muting configuration decided for thebase station 18, but note that the base station 18 also may transmitsome muting configuration information to the UEs 14, via lower-layersignaling.

In cases where the base station 18 or another node in the networkdecides the muting configurations to be used by the base station 18, thenode 24 “determines” the muting configuration of the base station 18based on receiving signaling from the base station 18 or from the othernode, where that signaling indicates the muting sequence and thereference point. Thus, in at least one embodiment, the node 24 isconfigured to determine the muting configuration for the base station 18based on receiving signaling from the base station 18 that indicates allor part of the muting configuration of the base station 18. Thoseskilled in the art will appreciate that the node 24 may receive mutingconfiguration signaling from a plurality of base stations 18.

Also, in embodiments where the node 24 is configured to determinecoordinated muting configurations for a plurality of base stations 18,the “coordinated muting configurations” may be reference points that arecomplementary between base stations 18, or may be muting sequences thatare complementary between base stations 18, or both.

In at least one such embodiment, the node 24 is configured to determinecomplementary muting configurations for the plurality of base stations18, based on directing different base stations 18 in the plurality ofbase stations 18 to use different muting sequences, or differentreference points, or different muting sequences and reference points. Inone example embodiment, the node 24 is configured to direct differentbase stations 18 to use different muting sequences by directing thedifferent base stations 18 to apply different cyclic shifts to the basesequence, to thereby derive, for each such base station 18, adifferently shifted version of the common base sequence.

FIG. 3 also illustrates an example embodiment of a UE 14, but thoseskilled in the art will recognize that the illustration and theteachings herein are broadly applicable to a wide range of wirelesscommunication apparatuses. The illustrated UE 14 is configured tomeasure reference signals transmitted by a network transmitter (e.g., bya given base station 18) for a given cell 20 in the network 10.

Correspondingly, the UE 14 comprises: a receiver configured to receivesignals transmitted by the network 10 for the given cell 20, includingsaid reference signals. Here, the receiver is included in theillustrated radio communication interface 50, which comprises a cellulartransceiver/modem in one or more embodiments, including the receiver forreceiving downlink transmissions from the network 10 and a transmitterfor transmitting uplink transmissions to the network 10. Forconvenience, the receiver is referred to as the “receiver 50” toindicate that it is part of the radio communication interface 50.

The UE 14 further includes one or more processing circuits 52—e.g.,digital processing circuitry—that include a measurement circuit 54 thatis configured to measure the reference signals (e.g., timing, quality,etc.), and a RS measurement and processing controller 56 (“controller56”) that is operatively associated with the receiver 50 and measurementcircuit 54. The controller 56 is configured to: determine a mutingsequence that indicates a muting pattern applied by the networktransmitter in transmission of the reference signals; determine areference point that indicates a reference timing for the mutingsequence applied at the network transmitter; determine muting occasionsat which the network transmitter mutes its transmission of the referencesignals, based on said muting sequence and said reference point; andcontrol the measurement circuit 54 to perform measurement of thereference signals from the network transmitter according to said mutingoccasions, such that the measuring circuit 54 does not measure thereference signals for the given cell 20 during said muting occasions. Inat least one embodiment, the UE is configured to acquire the mutingconfiguration from the received signaling, e.g. the assistance datareceived over LPP from E-SMLC.

In one or more embodiments, the controller 56 is configured to determinethe reference point according to one or a set of predefined System FrameNumber (SFN) values. These values may be pre-defined and thus may bepre-stored in memory in the UE 14 and/or signaled to the UE 14 by thenetwork 10.

Further, in one or more embodiments, the controller 56 is configured touse either the muting sequence or the reference point as a common valuefor determining the muting occasions for one or more neighboring cells20, and to control measurement of the reference signals from each suchneighboring cell 20 according to the respective muting occasionsdetermined for the neighboring cells 20.

Further, in one or more embodiments, the controller 56 is configured toreceive, via the receiver 50, assistance data from the network 10 thatindicates that the reference point is common to a number of cells 20identified in the assistance data, including the given cell 20, andwherein the reference point comprises a common reference point for thatnumber of cells 20, while each such cell 20 uses a unique mutingsequence that is signaled in the assistance data. For example, cells20-1, 20-2, and 20-3 all use a common reference point, but each uses adifferent muting sequence.

More broadly, in at least one embodiment, the controller 56 isconfigured to determine one or both of the muting sequence and thereference point based on the UE 14 receiving signaling from thetransmitter (e.g., a base station 10), or from another node in thewireless communication network, such as the node 24. Additionally oralternatively, the controller 56 is configured to determine one or bothof the muting sequence and the timing reference point based on readingpre-configured information from storage within the UE 14—e.g., fromnon-volatile memory within the UE 14.

Further, in at least one embodiment, the reference signals arepositioning reference signals (PRS) that are transmitted according to aknown periodicity, subject to muting at said muting occasions, and thecontroller 56 is configured to determine the muting sequence in use by agiven base station 18 for a given cell 20 by determining a sequence ofindicators or index values that indicate a muting pattern relative tosaid known periodicity.

Still further, in at least one embodiment, the controller 56 isconfigured to determine the muting sequence for a given cell 20 based onthe UE 14 receiving signaling indicating a cyclic shift that is appliedby the cell's transmitter to a base muting sequence and determining ashifted sequence used by the transmitter for the given cell 20, based onshifting the base muting sequence according to the indicated cyclicshift. That is, the base sequence is known a priori to the UE 14, orsignaled to it, and the UE 14 determines the shifted sequence actuallyin use for a particular cell 20 based on receiving signaling indicatinga shift relative to the base sequence, such that the shifted version ofthe base sequence can be determined by the UE 14.

With the above in mind, FIG. 4 illustrates one embodiment of a method400 implemented by a UE 14 or essentially any other wirelesscommunication apparatus. The method 400 is directed to determining whenreference signals are muted in a given cell 20 of the network 10. Themethod includes determining a periodic muting sequence indicating amuting pattern used for muting said reference signals in a cell 20 ofthe network 10 (Block 402), and determining a reference point relatingthe periodic muting pattern to a certain reference time (Block 404). Themethod further includes determining when the reference signals are mutedin the cell 20 according to the periodic muting sequence and thereference point (Block 406).

The method (400) also may include controlling reference signalmeasurements, in accordance with the determined muting times (Block408). For example, the UE 14 does not attempt to measure referencesignals for the cell 20 at the times when it has determined that thosesignals are muted. Of course, it will be understood that the UE 14 maybe making reference signal measurements for a cell 20 that is not muted,while avoiding such measurements for another cell 20 that is muted.

FIG. 5 illustrates a corresponding base station method 500, such as maybe carried out by any one or more of the base stations 18 illustrated inFIGS. 2 and 3, for example. The method 500 includes determining a mutingconfiguration for a cell 20 controlled by a base station 18 (Block 502).Here, the muting configuration of the cell 20 is defined at least inpart by a muting sequence comprising a pattern for muting referencesignals periodically transmitted for the cell 20. As noted, a basestation 18 may determine either the muting sequence or the referencepoint, or both, based on making its own decisions, or based oncooperating with one or more other base stations 18, or based onreceiving control signaling from the node 24 or another node in thenetwork 10 that has decided the muting configuration to be used by thebase station 18.

In either case, the method includes muting the reference signals for thecell 20 according to the muting configuration (Block 504). Exampledetails for the processing actions comprising Block 504 includedetermining whether it is (in general) time to transmit referencesignals according to the configured periodicity (Block 504A). If not,reference signal transmission is skipped (Block 504D). If so, thetransmitter determines whether muting applies to this particularreference signal transmission (Block 504B). In other words, should thetransmitter transmit the reference signals or mute them (which can beunderstood as a zero power or low power transmission). If this referencesignal transmission is a muting occasion according to the configuredmuting sequence and reference point, then the transmitter mutes thereference signals (Block 504D). If this is not a muting occasion, thenthe transmitter transmits the reference signals (Block 504C).

Turning to FIG. 6, one sees one embodiment of a method 600 such as maybe implemented in the node 24 illustrated in FIGS. 2 and 3, for example.Here, the method 600 begins with the node 24 determining the mutingconfigurations of one or more cells 18, where the muting configurationis defined by a muting sequence and a reference point (Block 602). Themethod continues with the node 24 generating assistance data for one ormore UEs 14, wherein the assistance data indicates the mutingconfigurations of the one or more cells 20 (Block 604). The methodcontinues with signaling (606) the assistance data to the one or moreuser equipments (14).

In one embodiment, the base station(s) associated with the one or morecells 20 decide the muting configurations of the cell(s) 20, and the“determining” of the cells' muting configurations by the node 24comprises the node 24 receiving signaling, e.g., from the base stations18, indicating the muting configurations as decided on by the basestations 18. In another embodiment, the node 24 “determines” the mutingconfigurations of the one or more cells 20, based on the node 24 beingthe entity that decides the muting configurations—in this regard, it maydecide the muting configuration of each cell 20 separately, or it mayperform a joint determination of (e.g., complementary) mutingconfigurations across a group of neighboring cells 20.

In at least one embodiment of the method 600, the node 24 is configuredto determine the muting configurations for one or more base stations 18from signaling received from those one or more base stations 18indicating the muting configurations. In at least one such embodiment,the node 24 receives signaling indicating a first muting configurationfor a first cell 20 and derives a second muting configuration for asecond cell 20, i.e., it derives a second muting configuration withrespect to the second cell 20. The node 24 performs the derivation basedon a transmission timing difference between the first and second cells20. In particular, the deriving the second muting configurationcomprises shifting a muting sequence of the first muting configurationby an amount dependent on the transmission timing difference, to obtaina shifted sequence to be used as the muting sequence of the secondmuting configuration. Here, it will be understood that the “mutingsequence” of a given muting configuration indicates a muting patternapplied to periodic transmission of reference signals for acorresponding cell 20

More generally, one or more of the nodes discussed herein may beconfigured to rearrange muting patterns with respect to a commonreference point. It should be clarified that the reference cell 20 maybe different for different UEs 14, and that rearranging therefore mayneed to be done per UE or per reference cell. In the latter case, therearranging can be reused for multiple UEs having the same referencecell. Whether the rearranging node is the node 24, or a base station 18,or a UE 14, it will be understood that the rearranging node generallyneeds to be informed, directly or indirectly, about the reference pointsof the muting patterns being rearranged and of the cell with respect towhich the patterns are being rearranged. Note also that the original andthe rearranged sequences described the same RS muting, just in differentways, so the transmissions/muting of RS is not affected by thearranging.

FIG. 7 illustrates a joint (cooperative) determination method 700, whichis implemented at the node 24, for example. Here, the node 24 identifiesa plurality of cells 20 (Block 702), e.g., the node 24 may beprovisioned with or otherwise receive neighbor list information, orother information indicating related subsets of cells 20. The methodcontinues with the node 24 determining a coordinated set of mutingconfigurations for the plurality of cells 20 (Block 704). Here,“coordinated” implies a complementary determination of mutingconfigurations across the plurality of cells 20—e.g., a common mutingsequence but unique reference points, or vice versa, or uniquecombinations of muting sequence and reference points across theplurality of cells 20. The method further includes sending signalingindicating the determined muting configurations (Block 706). Suchsignaling may be twofold: e.g., control signaling to the involved basestations 18, to inform them of the muting configurations decided for thecells 20, and assistance data signaling to UEs 14, which may be carriedtransparently through the base stations 18 to the UEs 14.

It is contemplated herein that, as an alternative, a given base station18 may function as a master base station for cooperatively determiningmuting configurations across a number of cells 20, even where one ormore of those cells 20 are controlled by one or more other base stations18. Further, a number of base stations 18 may cooperate to coordinatethe muting configuration decisions made for a group of cells 20, whereeach such base station 18 controls one or more of the cells 20 in thatgroup.

FIG. 8 depicts a related scenario, wherein the method 800 is implementedat the node 24, and wherein it is assumed that the base stations 18decide cell muting configurations, rather than the node 24. As such, theillustrated processing begins with the node 24 determining the mutingconfiguration of one or more cells 20, based on received signaling fromthe involved base stations 18 (Block 802), where that signalingindicates the muting configurations of the involved cells 20. Forexample, the signaling comprises messages that include fields or othersuch information elements that identify the muting sequence and/orreference point to be used by each cell 20.

The method 800 continues with the node 24 sending higher-layer signalingto radio receivers that are or will make reference signal measurementsfor the involved cells 20 (Block 804). For example, the node 24 sendshigher-layer signaling to the UEs 14 operating in the cells 20controlled by the base stations 18, or operating in adjacent cells 20.This aspect of operation is advantageous in the sense that the basestations 18 can decide the muting configurations to be used, but thenode 24 can still act as a centralized repository for receiving thatinformation and disseminating all or at least part of that information(via higher-layer signaling) to the UEs 14 that are or will be makingreference signal measurements in one or more of the involved cells 20.

Turning to further example details, FIG. 9 illustrates an example “basesequence” which may be used as the foundation for deriving a number ofuniquely shifted sequences, two examples of which are shown in FIG. 10.That is, one aspect of the muting configuration as taught herein is abase sequence of RS muting indicators, each applied to a certain timeinterval, where the sequence may be, for example, a sequence of binaryindicators (e.g., ‘01001’ where ‘1’=RS is muted, ‘0’=RS is not muted) ora sequence of indexes of the time intervals with RS muted (e.g., (2,5)for the same sequence example). It is straightforward that a sequence ofindexes can be converted to a corresponding sequence of binaryindicators and vice versa.

The certain time interval may, for example, be the minimum time unitover which the reference signal power is constant (e.g., symbol,subframe, several subframes, etc.). In LTE, the minimum time unit for RSconstant power may be either a subframe or a positioning occasion). Themuting periodicity (in the case of the binary sequence, the mutingperiodicity can be equal to the sequence length. In the case that mutingsequences are indicated using a sequence of indexes, the periodicity mayneed to be given explicitly.

As for the reference point, it may be understood in one or moreembodiments as either explicitly indicating the cyclic shift of thebaseline sequence or providing the information necessary for derivingit, so that the muting sequence in the measured time units can bededuced in the right order. More broadly, the reference point indicatesa logical start of the period of the muting sequence, where the logicalstart is not necessarily related to the time when the muting informationis received and from where it actually applies. Thus, in one or moreembodiments, the reference point is interpreted as the muting activationtime. In other embodiments, the reference point is interpreted as alogical reference. In such cases, it may be assumed by a receiver (e.g.,a UE 14) that the reference point applies from the first measurementopportunity after receiving muting configuration signaling withoutassuming that the same muting configuration has been already activatedin a previous measurement opportunity (unless the receiver has beeninformed about this earlier). In one or more other embodiments, thereference point is a relative offset value, e.g., a relative SFN offsetwith respect to the cell for which muting is defined or other cell whichmay be the reference cell. It will be understood that a reference cellserves as the reference for certain timing determinations, such as thoserelating to Reference Signal Time Difference (RSTD) measurements.

Also, as noted, the reference signals at issue herein may comprisepositioning reference signals, cell-specific reference signals, oressentially any type of reference or pilot signals, which aretransmitted by a radio network node and which can be muted at certaintimes by the radio network node. As an example, assume a base sequenceof length L, as shown in FIG. 9.

The sequence is denoted by M=(m₁, m₂, . . . m_(L-1), m_(L)) and hasperiodicity of L, and a reference point x. Therefore, the RS mutingconfiguration at time y (measured in time intervals in which the RSconfiguration applies, e.g., the reference signal transmissionperiodicity) is m_(((y−x)mod L)+1). The RS muting configuration over aninterval of length L starting at y can be obtained by cyclic shift of Mby ((y−x) mod L) elements to the left. See FIG. 10, illustrating amuting configuration propagated to y, based on the base sequence of FIG.9 and the reference point x.

The process of defining the RS muting configuration at point y isreferred to herein as “muting configuration propagation.” In oneembodiment of the present invention, the cyclic shift in the mutingconfiguration propagation is implemented as a multiplication modulo p(x)operation, where p(x) is the polynomial of x and x is used to describethe base RS muting sequence as a polynomial of degree L−1, i.e., m₁+m₂x+. . . +m_(L-1)x^(L-2), m_(L)x^(L-1).

It may be noted that by propagating the muting configuration in thismanner, it is always possible to find a cyclic shift of a given RSmuting sequence with respect to a new reference point that would beequivalent to the non-shifted (base) sequence and the initial referencepoint. In this manner, unique muting configurations may be propagatedfor a plurality of transmitting nodes. FIGS. 11 and 12 providenon-limiting examples of muting sequence propagation.

In FIG. 11, a base muting sequence is propagated (shifted) for cell “i”to account for the difference in time between the reference point of thebase sequence and the time of the next (periodic) reference signaloccasion after receipt of the muting configuration. For example, a UE orother wireless communication apparatus can propagate the base sequencebased on cyclically shifting the base muting sequence, to properly alignit pattern-wise with the ongoing, periodic reference signaltransmission. FIG. 12 illustrates a similar propagation, but where thepropagation is done in cell “j” with respect to a reference point forcell “i”.

Propagation may be done, for example, at the node 24 and/or at the UEs.The node 24 or another network node therefore may initiate the muting ofreference signals in one or more cells 20 (e.g., a group of serving andneighbor cells 20) and on any carrier frequency according to a mutingsequence with a certain periodicity at any point in time. On the otherhand the node 24 may provide the muting configuration information usedin the cells 20 to the UEs 14 any time after the muting is initiated inone or more cells 20. It is important that any given UE 14 knows whetherthe reference signals in a particular cell 20 are or are not muted forevery reference signal transmission occasion. This need requires thatthe UE 14 be aware of the start of the period of the muting sequence ineach cell 20, i.e., the reference point.

By the virtue of knowing the reference point and the mutingconfiguration information (i.e. periodicity of the sequence and theirmuting states, etc.), the UE 14 can derive the muting sequence currentlyused in each cell 20. As noted for one or more embodiments, the SFN orsome function of the SFN can be used as the reference point. Of course,the present invention does not preclude other bases for the referencepoint.

Assuming that the reference point is based on the SFN, a UE 14identifies the physical cell identity and is thus able to acquire theSFN for a given cell 20 by reading the broadcast channel (e.g., thephysical broadcast channel (PBCH) in E-UTRAN). In such an example, theSFN is a counter of 1024 values (from 0 to 1023), which indicates thecurrent frame number in a cell 20. (The counter rolls over, in that itrestarts at 0 upon reaching 1023.)

Having knowledge of the cell's SFN, the UE 14 determines the logicalstart point of the muting sequence in the cell 20 according to thereference point. The reference point in terms of the SFN may be providedto the UE in any number of ways. For example, there may be a common,predefined SFN value that serves as the reference point. In a variationof this approach, there may be more than one choice of SFN value to takeas the reference point, but the set of possible values is limited andpredefined. Alternatively, there may be defined mapping between the SFNvalue to take as the reference point and the cell 20 (e.g., anSFN-to-CELL ID mapping). As yet another alternative, the SFN value totake as the reference point may be signaled. Still further, the correctSFN value may be determined as SFN mod N. In one embodiment, N=16. Ofcourse, other values, such as N=4, may be used and these numericexamples are to be understood as non-limiting.

According to an embodiment based on a predefined, common value of SFN totake as the reference point, there is one such SFN value that ispredefined in the applicable wireless communication standard. In oneembodiment, the predefined value is common for all cells 20, includingthe serving/reference and the neighbor cells, i.e. in synchronizednetworks where the same SFN value will result in the same time in allcells.

A UE 14 therefore uses the predefined value as the reference time of thestart of the periodicity of the muting sequences in each cell 20. Anexample can be the predefined SFN value=0. Another example is of SFNvalue=511. Other predefined values may be selected, of course. Inasynchronous networks, a common reference point given by SFN should bedefined with respect to some cell, where an asynchronous network may bea network with frame-aligned cells, subframe-aligned cells, non-alignedcells or any mixture of cells that are differently aligned with respectto each other. A synchronous network is a network where all cells areSFN-aligned. This means that some adjustment of the muting sequences ofcells may need to be done in asynchronous networks, e.g., in thepositioning node, in order to adjust them to a common reference timebefore signaling to the positioning target (e.g. UE). The commonreference point may be signaled to the UE or may be pre-determined. Thepositioning target should either be able to acquire the timing of thecell with respect to which the common reference point has been definedor it should be able to adjust back the common reference point to thecells to be measured.

The predefined SFN value can be the same for all carrier frequencies.Alternatively the predefined SFN value can be different for each carrierfrequency. In any case, the predefined SFN(s) at which the RS mutingsequences start or repeat in the cells 20 is configured at theappropriate network nodes (e.g., at the base stations 18). For example,eNodeBs in an LTE network are programmed with the predefined SFNvalue(s) at setup. Such provisioning may be performed by an operationand maintenance (OAM) node or by a positioning server, or by essentiallyany other network node.

In cases where the reference point is interpreted as an activationfactor, having a single predefined reference point value has thefollowing drawback. Assuming a fixed reference point (SFN=0) is used,then network 10 may have to wait up to 1 SFN cycle (10.24 sec) to startthe RS muting for the first time. This worst-case delay is long inrelative terms. Using more than one SFN value as a possible referencepoint addresses this drawback. Thus, one approach taught herein is todefine a limited set of candidate SFN values as possible choices to usefor the reference point. For example, the reference point can be limitedto a few values, e.g. SFN=[0, 127, 511, 1023]. This approach requiresonly a small number of bits for signaling the selection, e.g., 2 bits tosignal one of four possible choices. The applicable wirelesscommunication standards would define the set of choices. Only one of theK predefined values would be signaled to any given UE 14 over the radiointerface, e.g. over LPP or RRC or using any other radio interfacesignaling protocol. The signaled value could be used as a commonreference point for a set of cells 20, e.g., for a group ofserving/reference and neighbor cells. In such a case, a UE 14 uses thepredefined value as the reference point for the start of the mutingsequence periodicity in each such cell 20.

An example predefined set of candidate SFN values is Ψ=[0, 127, 511 and1023]. For this example, 2 bits are required to indicate to UEs 14 whichspecific SFN is in use as the reference point, i.e. by indexing the setΨ. The predefined set of SFN values (Ψ) can be the same for all carrierfrequencies, or the predefined set of the SFN values (Ψ) can bedifferent for each carrier frequency. Also, the reference point (atwhich the reference signal muting sequence starts or repeats in a givencell 20 or cells 20 in the network 10) generally must be signaledbetween the base stations 18 and the one or more other network nodes,such as the node 24, which may be a positioning server, such as anE-SMLC in E-UTRAN. For example, a positioning server configures a giveneNodeB using the LPPa protocol, so that the eNodeB is provided with theSFN value to be used by the eNodeB for starting the muting sequence (asapplied to PRS transmitted by the eNodeB for one or more cells 20).

In another alternative mentioned above, an SFN-to-Cell mapping may beused as the basis for determining the SFN value to use as the referencepoint. In one such embodiment, the SFN used for the reference point ismapped to the cell-specific information, e.g. reference time is mappedto the cell identifier. More specifically the reference point is definedby a mapping between SFN values and cell identifiers. This mapping canbe predefined in the applicable wireless communication standard, forexample. Hence, after acquiring the cell identity of a cell 20, such asthe physical cell identity, a UE 14 can determine the SFN value to useas the reference point from the predefined mapping table. Anotherembodiment extends such mapping to cell groups, wherein the samereference point is mapped to a group of cells 20, e.g. when the groupingis based on the base station power class or any one or more othercriteria.

Rather than predefined values, the reference point may be signaled. Inone such embodiment, the reference point is signaled to UEs 14 in theassistance data for each cell 20 per (carrier) frequency, including theserving and the neighbor cells 20, and reference or non-reference cells20. In this case, the reference point can be different for differentcells 20 and different frequencies. More specifically, any possible SFNvalue can be used as the reference time and thus can be signaled to theUEs 14. This approach provides the fullest flexibility for usingessentially any SFN value as the reference point for any given cell 20in the network 10. As the SFN can take on 1024 values in E-UTRAN, onewould need 10 bits to signal the particular SFN value to use as thereference point. As a special case, a common value of SFN may be used asthe reference point across all carrier frequencies in a given cell 20,but different values can be used in different cells 20. And, asmentioned before, LPPa protocol signaling, or other such signaling, maybe conducted between a positioning node and the base stations, to shareor otherwise set the values to be used as the reference points.

In yet another embodiment contemplated herein, a positioning node, e.g.,an E-SMLC, aligns cell-specific reference points over multiple cells 20and frequencies to a generic one, while accordingly rearranging themuting configuration. One implementation of this approach uses themuting configuration propagation approach introduced earlier. That is,rearranged muting patterns may be cell-specific and thus signaledper-cell, while the reference point is common to all cells 20. In atleast one such embodiment, the processing circuitry of the positioningnode is configured to determine the alignment and rearrangement needed.

Having a generic reference point can be exploited to reduce thesignaling overhead by signaling the reference point information only forone cell 20, e.g., the reference cell (meaning a conditional inclusionof the reference point information in the assistance data). Morespecifically the reference point can, for example, be a single genericSFN value for all cells 20, for all carrier frequencies. The SFN valuecan be any value ranging from 0 to 1023 in E-UTRAN.

In another embodiment, the generic reference point is derived per(carrier) frequency. In this embodiment, the reference point can be asingle generic SFN value for all cells 20 on one carrier frequency.

In yet another embodiment aimed at reducing signaling overhead, thesignaled generic reference point can be derived as follows: thereference point=(SFN) mod (N); where N is an integer. A particularexample is reference point=(SFN) mod (16). Because the SFN (for E-UTRAN)ranges from 0 to 1023, the possible reference times for mod 16 include64 candidates, which can be signaled using a reduced number of bits.Such a reference point can be common for all cells 20 on all carrierfrequencies, or can be common for all cells 20, per carrier frequency.

As the reference point can be generic for all cells 20 or a group ofcells 20, so too can the muting sequences be common to more than onecell, or be cell-specific. In one embodiment, the common parameters aresignaled (or present) only for the reference cell 20 (and are assumed tobe used for the other cells 20). Cell-specific values are signaled orotherwise present for all cells 20 to which they apply. FIG. 13 providesan example table 60, showing that all or a group of cells 20 may use acommon reference point in combination with a unique muting sequence, ora unique reference point in combination with a common muting sequence,or may use unique reference points and muting sequences for each cell20.

When changing the reference point, e.g., from cell-specific to genericor the other way around, the muting configuration sequence has to berearranged accordingly by propagating the muting configuration asdescribed earlier. The rearrangement may be implemented in the basestation(s) 18, in the node 24, or elsewhere in the network 10.

Assuming no centralized control, the muting configuration is decided bythe base station 18 and signaled to a positioning node, for example. Themuting configurations received in the positioning node arecell-specific; thus, if a generic reference point is used, rearrangingof the muting configuration sequence before signaling it to thepositioning target (e.g. UE) is necessary. Consider the followingexample:

Given Cell 1 muting sequence ‘00010001’ with a reference point x, andgiven Cell 2 muting sequence ‘00010001’ with a reference point y. In asynchronous network, reference point x in Cell 1 corresponds to the sametime x in Cell 2. Assume the muting sequence of Cell 2 adjusted to thereference point a gives ‘01000100’. If x is the common reference pointfor both Cell 1 and Cell 2, then the network has to transmit ‘00010001’for Cell 1 and ‘01000100’ for Cell 2. In an asynchronous network,reference point x in Cell 1 may not correspond to the same time in Cell2. Assume reference time x of Cell 1 is decided to be the reference forboth Cells. Assume reference point x in Cell 1 corresponds to referencetime z in Cell 2. Furthermore, Cell 2 muting sequence adjusted toreference point z gives ‘00100010’. So, assuming reference point x to bethe common reference for both cells, the following information will bethen transmitted to the positioning target: ‘00010001’ for Cell 1 and‘00100010’ for Cell 2.

With the centralized control, the process is reversed. For example, thepositioning node decides a configuration, but then either the BSs, orthe positioning node before communicating to the BSs, may need to adjustthe sequences before applying the muting configuration e.g. from thecommon reference point to the cell-specific one. For example, in anasynchronous network, a positioning node may decide the configurationsequences per cell assuming they are synchronized (e.g. to keep thenetwork implementation simple). If the misalignment of a given cell 20with respect to the reference cell 20, or with respect to some referencetime, is known, then the rearrangement can be done in the base stations18, for example.

As another example:

In an asynchronous network, assuming the same reference point x, Cell 1and Cell 2 have muting sequences ‘00010001’ and ‘00100010’,respectively. However, Cell 1 and Cell 2 may or may not understand thecommon reference point and may relate it to their own timing. In suchcases, the positioning node may have to convert to cell-specific mutingconfigurations before sending them to the BSs. For example, it mayadjust for the cell-specific reference points known to the cells, e.g.,use cell-specific reference point x for Cell 1 and cell-specificreference point x for Cell 2 (since the network is synchronous, the tworeference points may correspond to different times in the two cells).

With such example variations in mind, it will be appreciated that thevarious embodiments of the present invention apply to a range ofreference signal types, including PRS. In the PRS case, mutingconfigurations may be specified with one subframe or one positioningoccasion as the smallest time unit. In any case, at least the followingsignaling enhancements are provided by one or more embodiments of thepresent invention:

Signaling from a LCS server to a LCS target, for example, from apositioning server (e.g., E-SMLC or SLP in LTE) to a UE;

Signaling from a radio node (e.g., eNodeB, beacon, relay, etc) to a LCSserver

No central coordination: RS muting information is signaled,

Central coordination: an indicator in the request for the mutinginformation is signaled;

Signaling from a LCS server to a radio node

No central coordination: An indicator in the request for the mutinginformation is signaled, and such indicator could trigger either animmediate reporting from the radio node, or the LCS server couldconfigure the reporting with alternative reporting criteria (i.e. not ondemand), so that the radio node could trigger the reporting of RS mutinginformation, for example, whenever it is modified;

Central coordination: RS muting information is signaled; this requiresthe radio node to be aware of the LCS server and implies the existenceof procedures to pre-exchange configuration information between LCSserver and radio node;

Signaling from a radio node to another radio node (e.g., for the RSmuting configuration exchange and distributed coordination between theradio nodes);

In case there are multiple positioning nodes (e.g. between any two ormore of E-SMLC, SLP, GMLC, etc.), signaling between the positioningnodes to enable exchange of the muting information, e.g., the genericreference point; and

Signaling from OAM system (i.e. NMS or DMS) or other network node (MME,SON nodes, etc.) to LCS server and/or radio node.

Consider an example of signaling between a radio node (e.g., a station18) and a LCS server (e.g., node 24) without central coordination. TheE-SMLC as said LCS server sets an indicator in an LPPa OTDOA InformationExchange Request to request ‘PRS Muting Configuration’ immediately(without further configuring any reporting criteria) and an eNodeBreplies with LPPa OTDOA Information Exchange Response where PRS MutingInformation IE is included. This information element contains the RSMuting Information. The E-SMLC sets an indicator in the LPPa OTDOAInformation Exchange Request to request ‘PRS Muting Configuration’ andadditionally configures reporting criteria (new IE ‘Reporting Criteria’)to inform the eNodeB it requires new reports if the information shouldchange in the future. A new procedure OTDOA Information Report is addedto LPPa to support the additional reporting. The eNodeB reportsimmediately after the first request and also whenever the information ischanged.

As an example of signaling between a LCS server and radio node withcentral coordination, an E-SMLC and eNodeB exchange configurationinformation beforehand via LPPa, so that eNodeB becomes aware of allapplicable E-SMLCs and they establish a permanent or semi-permanentassociation. (Note that this behavior would be a changed in the current3GPP positioning architecture.) Then, the E-SMLC distributes concernedRS muting information to involved eNodeBs.

Further signaling examples include the contemplated signaling betweenradio nodes, such as to support the exchange of muting configurationinformation between such nodes and/or to support the cooperativedetermination of muting configurations between nodes. As a particularexample, RS Muting Information is added to the X2AP protocol, namely tothe X2 Setup and eNodeB Configuration Update procedures, to enable suchexchanges between eNodeBs in an LTE network, via the X2 interface.

Other signaling contemplated herein relates to OAM retrieval. Forexample, RS Muting Information is provided by an eNodeB to an OAM systemwithin a wireless communication network, for retrieval by the applicableLCS server, which may be an E-SMLC or an SLP.

With such signaling in mind, and in view of the foregoing examples, thepresent invention will be understood as offering a number of advantages,including but not limited to these items: flexible muting configurationwith simple, low-overhead signaling; no need for predefined PRS mutingpatterns; and reduced UE complexity (no need for blind detection of RS),processing, power consumption, in combination with improved positioningperformance.

These and other advantages are realized through various aspects of thepresent invention, including the definition of a cell's mutingconfiguration as a muting sequence defining a muting pattern applied toor overlaid on an underlying reference signal transmission periodicity,and a reference point that indicates or identifies a virtual startingpoint for relating the muting sequence to the reference signaltransmissions—i.e., the reference point indicates or allows for thedetermination of a logical starting point for the muting sequence as itapplies to reference signal transmissions in a given cell. With thisapproach, reference points may be cell-specific or generic (common) to anumber of cells and, likewise, muting sequences may be cell-specific orgeneric. One advantageous implementation provides for conditionalsignaling of a generic reference point for the reference cell only.

Further, for the case with no central control of RS mutingconfigurations, a positioning node (e.g., and E-SMLC or SLP) isconfigured to rearrange cell-specific base sequences.

Of course, the present invention is not limited to the foregoingfeatures and advantages. Rather, the present invention is limited onlyby the claims and their legal equivalents.

What is claimed is:
 1. A method in a base station of determining timeswhen periodically-transmitted reference signals are muted in a cell of awireless communication network, said method comprising: determining amuting configuration for the cell controlled by the base station, saidmuting configuration defined at least in part by a predefined value of areference cell's System Frame Number (SFN) and a muting sequencecomprising a pattern for muting reference signals periodicallytransmitted for the cell; and muting the reference signals for the cellaccording to the muting configuration.
 2. The method of claim 1, whereinthe cell for which the reference signals are muted according to themuting configuration is not the reference cell, and wherein thereference cell serves as a reference for certain timing determinationsat one or more user equipments in the cell.
 3. The method of claim 1,wherein said reference signals are transmitted at periodic referencesignal occasions, and wherein the muting sequence comprises a sequenceof indicators in assistance data transmitted to one or more userequipments, wherein each indicator represents a given reference signaloccasion and indicates whether muting will be applied for that givenreference signal occasion.
 4. The method of claim 3, wherein thepredefined value of a reference cell's SFN relates the muting sequenceto a certain reference time by logically associating a first indicatorin the muting sequence with a first reference signal occasion thatstarts after the beginning of SFN=0 in the reference cell.
 5. The methodof claim 1, wherein the muting configuration is determined autonomouslyfor the cell or jointly for the cell in conjunction with one or moreneighboring cells, and wherein the method further comprises: signalingthe muting configuration for the cell to another node in the wirelesscommunication network.
 6. The method of claim 5, wherein the other nodecomprises a positioning node, and wherein the base station is configuredto signal the muting configuration for the cell to the positioning nodeaccording to a defined positioning signaling protocol.
 7. The method ofclaim 1, wherein the muting configuration for the cell is decided at apositioning or operations and maintenance node in the wirelesscommunication network, and wherein the base station is configured todetermine the muting configuration from signaling received from thepositioning or operations and maintenance node.
 8. A base stationconfigured for use in a wireless communication network, said basestation comprising: a radio communication interface configured totransmit signals, including reference signals periodically-transmittedfor a cell; and a controller operatively associated with the radiocommunication interface, and configured to: determine a mutingconfiguration for the cell controlled by the base station, said mutingconfiguration defined at least in part by a predefined value of areference cell's SFN and a muting sequence comprising a pattern formuting the reference signals; and mute the reference signals for thecell according to the muting configuration.
 9. The method of claim 8,wherein the cell for which the reference signals are muted according tothe muting configuration is not the reference cell, and wherein thereference cell serves as a reference for certain timing determinationsat one or more user equipments in the cell.
 10. The method of claim 8,wherein said reference signals are transmitted at periodic referencesignal occasions, and wherein the muting sequence comprises a sequenceof indicators in assistance data transmitted to one or more userequipments, wherein each indicator represents a given reference signaloccasion and indicates whether muting will be applied for that givenreference signal occasion.
 11. The method of claim 10, wherein thepredefined value of a reference cell's SFN relates the muting sequenceto a certain reference time by logically associating a first indicatorin the muting sequence with a first reference signal occasion thatstarts after the beginning of SFN=0 in the reference cell.
 12. The basestation of claim 8, wherein the controller of the base station isconfigured to determine the muting configuration by determining themuting configuration autonomously for the cell or jointly for the cellin conjunction with one or more neighboring cells, the base stationfurther comprising a communication interface configured for signalingthe muting configuration for the cell to another node in the wirelesscommunication network.
 13. The base station of claim 12, wherein theother node comprises a positioning node, and wherein the controller ofthe base station is configured to signal, via the communicationinterface, the muting configuration for the cell to the positioning nodeaccording to a defined positioning signaling protocol.
 14. The basestation of claim 8, wherein the muting configuration for the cell isdecided at a positioning or operations and maintenance node in thewireless communication network, and wherein the controller of the basestation is configured to determine the muting configuration fromsignaling received from the positioning or operations and maintenancenode.
 15. A method in a positioning node configured for operation in awireless communication network, said method comprising: determining amuting configuration for each of one or more cells of the wirelesscommunication network, wherein the muting configurations of the one ormore cells control the times when muting is applied to reference signalsperiodically transmitted in each of the one or more cells and whereineach of the muting configurations are defined at least in part by apredefined value of a reference cell's SFN and a muting sequencecomprising a pattern for muting the periodically transmitted referencesignals; generating assistance data for one or more user equipments,said assistance data indicating the muting configurations of the one ormore cells; and signaling the assistance data to the one or more userequipments.
 16. The method of claim 15, wherein determining the mutingconfigurations comprises determining the muting configurations fromsignaling received from one or more base stations indicating the mutingconfigurations.
 17. The method of claim 16, wherein determining themuting configurations from the signaling received from the one or morebase stations comprises receiving signaling indicating a first mutingconfiguration for a first cell and deriving a second mutingconfiguration for a second cell based on a transmission timingdifference between the first and second cells, wherein deriving thesecond muting configuration comprises shifting a muting sequence of thefirst muting configuration by an amount dependent on the transmissiontiming difference to obtain a shifted sequence to be used as the mutingsequence of the second muting configuration, and wherein the mutingsequence of a given muting configuration indicates a muting patternapplied to periodic transmission of reference signals for thecorresponding cell.
 18. The method of claim 15, wherein determining themuting configurations comprises the positioning node deciding the mutingconfigurations to be used for each of the one or more cells, the methodfurther comprising: sending control signaling to one or more basestations associated with the one or more cells to cause the one or morebase stations to adopt the muting configurations decided by thepositioning node.